#include<stdio.h>
#include <stdlib.h>
 int main() {

    int i,j;

    int x = 1 ;
    int y = 20;
    int velocity = 1;
   while (1)
  {
        if ( x>20 || x<1 )
        {
            velocity = (-1)*velocity ;
        }
        x = x + velocity ;
        system("CLS");
        for (i=0;i<x;i++)
        printf("\n");
        for (j=0;j<y;j++)
        printf(" ");
        printf("0\n");
        }

    return 0;
}
